.\"	$NetBSD: pidfile.3,v 1.13 2011/03/29 13:55:37 jmmv Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe.
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.Dd March 23, 2011
.Dt PIDFILE 3
.Os
.Sh NAME
.Nm pidfile
.Nd write a daemon pid file
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In util.h
.Ft int
.Fn pidfile "const char *path"
.Sh DESCRIPTION
.Fn pidfile
creates a file containing the process ID of the caller program.
The pid file can be used as a quick reference if
the process needs to be sent a signal.
When the program exits, the pid file is removed automatically, unless
the program receives a fatal signal.
.Pp
If
.Ar path
is
.Dv NULL
or a plain basename (a name containing no directory components), the pid file
is created in the
.Pa /var/run
directory.
The file name has the form
.Pa /var/run/basename.pid .
The basename part is either the value of
.Ar path
if it was not
.Dv NULL ,
or the program name as returned by
.Xr getprogname 3
otherwise.
.Pp
If
.Ar path
is an absolute or relative path (i.e. it contains the
.Sq /
character),
the pid file is created in the provided location.
.Pp
Note that only the first invocation of
.Fn pidfile
causes a pid file to be written; subsequent invocations have no effect
unless a new
.Ar path
is supplied.
If called with a new
.Ar path ,
.Fn pidfile
will remove the old pid file and write the new one.
.Sh RETURN VALUES
.Fn pidfile
returns 0 on success and -1 on failure.
.Sh SEE ALSO
.Xr atexit 3
.Sh HISTORY
The
.Fn pidfile
function call appeared in
.Nx 1.5 .
Support for creating pid files in any arbitrary path was added in
.Nx 6.0 .
.Sh BUGS
.Fn pidfile
uses
.Xr atexit 3
to ensure the pid file is unlinked at program exit.
However, programs that use the
.Xr _exit 2
function (for example, in signal handlers)
will not trigger this behaviour.
